> you can use up all available memory in approx. 64 quick steps by: Type 1 character; Undo to beginning; Type 1 character; Undo to beginning; etc This is fine

> you can use up all available memory in approx. 64 quick steps by: Type 1 character; Undo to beginning; Type 1 character; Undo to beginning; etc This is fine because "undo to beginning" isn't a single action. Each time this loop runs, the user spends more and more time mashing undo to get back to the beginning. The number of actions in the history is only increasing by a constant amount per user action.